Hyperacute rejection ofthe heart and kidney is reliably prevented when GalTKO organs are used that additionally express a human complement pathway regulatory protein (hCPRP). In contrast, although GalTKO.hCPRP pig lung xenograft function is significantly prolonged relative to GalTKO or hCPRP lungs, lung injury nonetheless occurs within hours of transplantation into baboons or following perfusion with human blood. Similarly, platelet sequestration occurs almost immediately when GalTKO.hCPRP pig livers are orthotopically transplanted in baboons, and limits recipient survival. A number of molecular incompatibilities between pig endothelial membrane glycoproteins and primate platelet receptors and plasma coagulation pathway proteins probably explain the mechanistic basis of coagulation pathway dysregulation and platelet sequestration in lung and liver xenograft injury. These incompatibilities may also contribute to related problems in heart and kidney xenotransplants, thrombotic microangiopathy (TM) and consumptive coagulopathy (CC). In this Project we will take advantage ofthe GalTKO.hCPRP pig lung's particular avidity for platelet and neutrophil sequestration, and its propensity to amplify coagulation pathway activation. Using a combination of clinically available approaches to impact thromboregulation (DDAVP, to deplete donor vWF pretransplant;zanamivir, a sialydase inhibitor, to maintain sialic acid expression on circulating platelet receptors and associated vWF) and unique molecular targeting reagents (an anti-GPlB Fab and an antisialydase antibody), Aim 1 will test the hypothesis that GPlB/vWF, modulated by desialydation, mediate primate platelet and neutrophil sequestration by porcine endothelium. In Aim 2, GalTKO.hCPRP pig lungs that also express human thrombin pathway regulatory proteins (thrombomodulin or endothelial protein C receptor) will reveal whether molecular incompatibilities in this pathway contribute significantly to lung injury, and whether expression of these molecules is protective. Aim 3 will determine whether strategies arising from Aims 1 and 2 will consistently yield life-supporting function of a pig lung in a baboon, and whether a similar approach reliably prevents thrombocytopenia in a baboon supported by a GalTKO.hCPRP pig liver.